This invention relates to kidney perfusion solutions and a method for increasing the viability of perfused kidneys prior to transplantation.
Kidneys must be preserved for a period of at least 5 hours prior to transplantation to obtain proper pathology assessment of the suitability of the organ for transplantation. Lack of proper preservation leads to degradation of organ function due to thrombosis (blood clotting), ischemia (lack of oxygen), or ischemia followed by reperfusion (the restoration of blood flow upon transplantation). These events bring about inflammation, cell death, and eventually failure of the organ. The preferred method for preserving kidneys is pulsatile preservation.
Pulsatile kidney preservation is a process in which the renal artery is connected to a kidney perfusion machine in order to simulate the normal process by which nutrients are supplied to the kidney. A solution is continuously perfused through a closed circuit which includes the kidney, which is typically maintained at 5 degrees C. In order for pulsatile preservation to be an effective method for preservation of xe2x80x9cextended criteriaxe2x80x9d organs (i.e., organs which are less optimal than those currently accepted for transplantion), the technician needs to monitor closely not just perfusion pressure, flow, and vascular resistance, but also the organ""s chemistries, including base excess, oxygen saturation, calcium, potassium, hematocrit, pO2, pH, and bicarbonate. This method has become the standard of care for kidney transplantation, due to its efficacy and cost effectiveness. See Light et al., xe2x80x9cImmediate function and cost comparison between static and pulsatile preservation in kidney recipients,xe2x80x9d Clin. Transplantation 233-236 (1996).
Although pulsatile perfusion of kidneys is superior to static preservation methods, pulsatile perfusion suffers from several drawbacks. It requires continuous monitoring and correction of chemistries as well as pressure and flow in order to be optimal, and thus the process is time- and labor-intensive (and hence expensive). Moreover, organ perfusion requires extensive expertise, and results can vary from perfusionist to perfusionist. Another problem that is observed with current kidney perfusion solutions is the rapid oxidation of glutathione, a key component of current kidney perfusion solutions that serves as an antioxidant. Finally, pulsatile preservation has only proven marginally effective at preserving organs from xe2x80x9cextended criteriaxe2x80x9d donors.
Nitric oxide (NO) can have both beneficial and detrimental effects in the kidney. A low level of NO, produced by the so-called constitutive nitric oxide synthases (NOS), found in endothelial cells (NOS3; ecNOS) or neurons and some other cell types (NOS1; nNOS), appears to be necessary for the maintenance of homeostasis in the kidney. See, for example, Kone et al., xe2x80x9cBiosynthesis and homeostatic roles of nitric oxide in the normal kidney,xe2x80x9d Am. J. Physiol. F561-578 (1997) and Radermacher et al., xe2x80x9cImportance of NO/EDRF for glomerular and tubular function: studies in the isolated perfused rat kidney,xe2x80x9d Kidney Int. 1549-1559 (1992). However, it has also been reported that high levels of NO produced by the inducible nitric oxide synthase (NOS2) during the process of kidney damage and/or transplantation are detrimental to the kidney, Klahr et al., xe2x80x9cRenal disease: The two faces of nitric oxide,xe2x80x9d Lab. Invest. 1-3 (1995). All three isoforms of NOS (NOS1, NOS2, and NOS3) are found in the kidney, though not all of their functions are known. See, for example, Kone et al, xe2x80x9cLocalization and regulation of nitric oxide synthase isoforms in the kidney,xe2x80x9d Semin. Nephrol. 230-241 (1999).
Transplant patients are often treated with immunosuppressive agents such as cyclosporine A in order to prevent transplant rejection. Such immunosuppressive agents can suppress nitric oxide production in the normal kidney, and thus can suppress certain kidney functions. See Bloom et al, xe2x80x9cAn experimental study of altered nitric oxide metabolism as a mechanism of cyclosporin-induced renal vasoconstriction,xe2x80x9d Br. J. Surg. 195-198 (1995) and Gaston et al., xe2x80x9cCyclosporine inhibits the renal response to L-arginine in human kidney transplant recipients,xe2x80x9d J. Am. Soc. Nephrol. 1426-1433 (1995).
Nitric oxide donor chemicals are known, and have proven safe and efficacious at modulating various physiological and pathological parameters associated with the presence of nitric oxide. The nitric oxide donor chemical S-nitrosoglutathione (GSNO) has been reported to reduce platelet aggregation both in vitro and in vivo, to reduce acute myocardial infarction and unstable angina, to be of therapeutic benefit to patients with the HELLP syndrome and in fetal pre-eclampsia, to inhibit platelet activity in patients undergoing percutaneous transluminal coronary angioplasty (PTCA) or saphenous vein grafts, and to inhibit vasospasm in human coronary arteries. GSNO was found to suppress thrombosis in a porcine model of balloon angioplasty and subsequent endovascular radiation, see Vodovotz et al., xe2x80x9cS-nitrosoglutathione reduces non-occlusive thrombosis rate following balloon overstretch injury and intracoronary radiation of porcine coronary arteries,xe2x80x9d 48 Int. J. Radiat. Oncol. Biol. Phys. 1167-1174 (2000).
Sodium nitroprusside, another nitric oxide donor chemical, has recently been suggested for addition to static liver perfusion solution. Rodriguez et al., xe2x80x9cRole of sodium nitroprusside in the improvement of rat liver preservation in University of Wisconsin solution: A study in the isolated perfused liver model,xe2x80x9d 87 J.Surg.Res. 201-208 (1999).
An object of the present invention is to preserve kidneys that have been taken from donors prior to transplantation into a recipient, by providing the low levels of nitric oxide necessary for optimal kidney function (essentially substituting for reduced levels or activity of NOS1 or NOS3), while inhibiting over-exuberant enzymatic production of NO from NOS2 that can damage the kidney.
A feature of the present invention is the presence of a nitric oxide donor chemical and a chemical inhibitor selective for the inducible isoform of nitric oxide synthase (NOS2) in a kidney pulsatile perfusion solution.
An advantage of the present invention is that it should permit the transplantation of kidneys from donors whose kidneys are less optimal than those accepted currently (xe2x80x9cextended criteriaxe2x80x9d organs).
Use of a particular nitric oxide donor chemical, GSNO, would have an additional advantage in that it would generate oxidized glutathione in addition to nitric oxide. This oxidized glutathione, if given simultaneously with an additional reagent that could reduce glutathione back to its bioactive form (such as the enzyme glutathione reductase as well as the necessary cofactors for the activity of this enzyme) would yield higher levels of bioactive glutathione.
In one aspect, the present invention is directed to a kidney pulsatile perfusion solution comprising at least one gluconate salt, glutathione, a nitric oxide donor chemical, and a chemical inhibitor selective for the inducible isoform of nitric oxide synthase.
In another aspect, the present invention relates to an improved process for perfusing a kidney with an amount of a nitric oxide donor chemical in an amount sufficient to mimic enzymatic production of nitric oxide by the beneficial enzymes NOS1 or NOS3, while preventing generation of an excessive amount of nitric oxide by NOS2.
In a third aspect, the present invention is directed to a method for increasing the availability of bioactive glutathione in a perfusion solution by including an additional reagent to reduce glutathione back to its bioactive form.